Methanol from biomass gasification

Abstract

1. A process (100) for the synthesis of methanol (1), comprising: subjecting a biomass feedstock (2) to a gasification process (6) in the presence of steam (5) and an oxidant (48); subjecting the gasifier stream (7) thus obtained to a water-gas shift conversion (10) and purification (14) to obtain a synthesis gas (15) carrying hydrogen, carbon monoxide and CO2; mixing said synthesis gas (15) with a second stream of synthesis gas (31) to obtain a third stream of synthesis gas (16); feeding said third stream of synthesis gas (16) to a methanol synthesis loop (19) to produce crude methanol (20) and a tail gas (35) carrying methane; and subjecting said tail gas (35) to a reforming step (25) in the presence of an oxidant (49) to produce said second stream of synthesis gas (31).

Description

[Technical field]

[0001] The present invention is in the field of methanol production. In particular, the present invention relates to a process and a plant for the synthesis of methanol. [Background technology]

[0002] The gasification process involves the partial oxidation of a carbonaceous feedstock in the presence of substoichiometric amounts of an oxidant such as oxygen or air. The products of gasification are synthesis gas, consisting of carbon monoxide, hydrogen and small amounts of carbon dioxide, water and methane, as well as a solid residue that is not completely combusted or oxidized.

[0003] There is growing interest in the art in using syngas obtained from the gasification of biomass to produce biomethanol. Biomass gasification is a complex process in which conflicting requirements must be taken into account, such as the need to avoid melting unburned residues and the need to keep the methane and carbon dioxide contents in the syngas as low as possible.

[0004] Melting of the unburned residues must be prevented to prevent impurities such as sulfur and alkalis from migrating into the synthesis gas, which could cause problems with the deactivation of the methanol synthesis catalyst and corrosion problems for the plant. Conversely, methane production must be limited, since this gas product does not participate in the methanol synthesis.

[0005] Conventional biomass gasification processes are typically carried out at relatively low temperatures, for example below 1000° C., and at medium to high pressures, typically comprised between 30-100 bar, in the presence of oxygen and water steam.

[0006] Unfortunately, as a result of the low temperature and high pressure operating conditions employed, the synthesis gas obtained from the process retains a relatively high concentration of methane, for example about 10-12 mole % calculated on a dry basis.

[0007] Large amounts of methane retained in the synthesis gas are a disadvantage because they adversely affect plant productivity and efficiency, since unconverted methane is not utilized in the process and is typically vented from the synthesis loop as tail gas and flared.

[0008] A further drawback that exacerbates the cost and energy efficiency of the bio-methanol process relates to the utilization and purification of the aqueous streams produced during the process.

[0009] In particular, methanol is obtained from the synthesis loop as a crude stream containing impurities, i.e. dissolved gases such as methane, higher alcohols, aldehydes, ketones and water, and must be purified downstream of the synthesis loop to obtain a high purity product. Purification is usually carried out in a distillation section, where the high purity methanol product is separated from an aqueous stream contaminated with residual methanol and streams containing the above mentioned impurities.

[0010] Said aqueous stream cannot be discharged directly to the environment but must be treated in a suitable unit, such as a scrubber, to reduce the CH3OH content. Obviously, said purification step increases the operating costs of the process and also involves a waste of resources, since the aqueous stream so obtained is then discharged from the plant.

[0011] Therefore, in view of the above considerations, it is highly desirable to develop methanol synthesis processes and plants that are energy efficient, economically viable and resource efficient.

[0012] US Pat. No. 5,399,433 discloses a hybrid plant for producing liquid fuels from a stream containing hydrogen and carbon monoxide produced by gasification of a solid carbonaceous feedstock and steam reforming of light fossil fuels. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] US Patent Application Publication No. 2014 / 0145819 Summary of the Invention

[0014] The object of the present invention is to overcome the drawbacks of the prior art.

[0015] The present invention is based on the insight that all resources produced during the synthesis, such as methane and aqueous streams, are recycled within the process to obtain a resource- and energy-efficient bio-methanol process.

[0016] Thus, one aspect of the present invention is a process for the synthesis of methanol as claimed in claim 1.

[0017] The process involves feeding the synthesis gas effluent from the gasification of biomass and from the reforming of the tail gas to a methanol synthesis loop in which catalytic conversion of carbon oxides to methanol is carried out under methanol synthesis conditions to obtain a methanol product and a methane-rich tail gas, which is partially recycled to the reformer for further conversion to synthesis gas.

[0018] A further aspect of the invention is a plant for producing methanol as claimed.

[0019] The plant comprises a front end for producing a first stream of syngas from gasification of biomass, a methanol synthesis loop for producing crude methanol and a methane-rich tail, and a tail gas processing section including a reforming unit for converting methane retained in the tail into a second stream of syngas. The first stream of syngas obtained from gasification and the second stream of syngas obtained from reforming are mixed to form a third stream of syngas, which is conveyed to the methanol synthesis loop.

[0020] The present invention provides an energy-efficient and economically viable option for producing biomethanol, since the methane synthesized as waste during gasification can be converted into a useful stream in a reformer, i.e. a second stream of syngas, which can then be converted into methanol, increasing the productivity of the plant.

[0021] A further advantage is that efficient recycling of the aqueous streams produced in the plant is achieved, eliminating the need for methanol purification treatment of said aqueous streams. Yet another advantage is that since water import and export are balanced, no water is lost within the plant, i.e. all produced water is recycled within the process. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 shows a schematic process layout of a methanol plant according to a preferred embodiment for the realization of the present invention. [Diagram 2] FIG. 2 shows a schematic process layout of a methanol plant according to an alternative embodiment of the present invention. [Diagram 3] FIG. 2 shows a schematic process layout of a methanol plant according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The term biomass in this invention includes, but is not limited to, woody materials (bark, chips, scraps, and sawdust), pulp and paper industry residues, agricultural residues, organic municipal materials, sewage, manure, and food processing by-products.

[0024] In the process of the present invention, the biomass feedstock is fed to a gasification process in the presence of steam and an oxidant to produce a gasifier stream, which is then subjected to a water-gas shift conversion and purification process to obtain a first stream of synthesis gas carrying hydrogen and carbon monoxide.

[0025] The resulting first stream of synthesis gas is mixed with a second stream of synthesis gas to obtain a third stream of synthesis gas, the second stream of synthesis gas being obtained by subjecting a tail gas extracted from the methanol synthesis loop to a reforming process.

[0026] The third stream of synthesis gas is then sent to a methanol synthesis loop where crude methanol is produced by catalytic conversion of carbon oxides to methanol under methanol synthesis conditions to obtain crude methanol and a methane-carrying tail gas.

[0027] The tail gas extracted from the methanol synthesis loop is fed to a reforming step in the presence of an oxidant to produce a second stream of syngas which is then mixed with the first stream of syngas obtained from the gasification unit.

[0028] According to a preferred embodiment, the biomass before being fed to the gasifier process is subjected to a series of pretreatments to improve the efficiency of gasification, including drying, pyrolysis and / or torrefaction.

[0029] Gasification is carried out in the presence of water steam to increase the hydrogen content in the synthesis gas, and in the presence of an oxidant, preferably oxygen. The oxygen can be produced on-site by an air separation unit or using a water electrolyser. Preferably, the oxygen stream has a purity of greater than 99 mol%, or preferably greater than 99.5 mol%.

[0030] After gasification, the synthesis gas obtained can have the following composition: a hydrogen content H2 comprised between 55 and 65 mol%, preferably equal to or about 61.1 mol%, a nitrogen content N2 comprised between 0.2 and 0.5 mol%, preferably equal to or about 0.4 mol%, a carbon monoxide CO content comprised between 22 and 28 mol%, preferably equal to or about 25.6 mol%, a carbon dioxide CO2 content comprised between 2 and 4 mol%, preferably equal to or about 3.4 mol%, a methane CH4 content comprised between 8 and 10 mol%, preferably equal to or about 9.5 mol%, an Ar content between 0.02 and 0.05 mol%, preferably equal to or about 0.04 mol%.

[0031] Methanol synthesis catalysts are usually sensitive to tar, particulates, sulfur, excess CO2, and other impurities such as sulfur, so a gas washing section can be provided after the gasification step.

[0032] According to a particularly preferred embodiment, the gasifier stream exiting the gasification section may be subjected to a water-gas shift conversion to adjust the H2 / CO ratio.

[0033] The gas exiting the water gas shift conversion may be subjected to a cooling step before being conveyed to the CO2 removal step. The CO2 removal may be carried out by known processes and techniques, i.e., selexol, rectisol, MEA or MDEA chemical absorption, etc.

[0034] According to the present invention, the tail gas leaving the methanol synthesis section is subjected to a reforming step, which is preferably carried out in the presence of an oxidizing agent under autothermal reforming conditions or partial oxidation conditions. Preferably, the reforming step is carried out at a temperature of 1000-1500°C, or 1000-1300°C.

[0035] Preferably, the concentration of inert gas in the synthesis loop is less than 40 mole %.

[0036] According to a particularly preferred embodiment, the tail gas reforming step comprises a pretreatment of the tail gas before the reforming reaction. Particularly preferably, the tail gas extracted from the methanol synthesis loop is subjected to a saturation step with water before the reforming process in order to obtain a saturated stream. More preferably, the saturated stream is further contacted with steam to obtain a conditioned stream, which is conveyed to the reforming step. Preferably, said conditioned stream is characterized in that it has a steam to carbon ratio S / C comprised between 1.0 and 2.0.

[0037] According to another particularly preferred embodiment, the crude methanol is subjected to a purification step to produce a methanol product, a first stream of fusel oil, a second stream of light ends hydrocarbons, and a recovered aqueous stream.

[0038] Preferably, said recovered aqueous stream is fed to said saturation step. Advantageously, all contaminated water produced in the plant is recycled in the process and no additional water treatment is required to purify the water. Moreover, an efficient utilization of resources is achieved.

[0039] Preferably, said conditioned stream obtained after mixing with the saturated water stream is further treated in a pre-heating step to obtain a temperature-conditioned stream having a temperature comprised in the range of 600°C to 750°C, or preferably equal to or around 650°C.

[0040] According to one embodiment of the invention, a further product of the methanol synthesis loop is a mixture of flash and tail gases, and said preheating stage is carried out under direct combustion conditions and is combusted by the first stream of said fusel oil, by the second stream of said light ends hydrocarbons and by the mixture of said flash and tail gases.

[0041] Hereinafter, the term fusel oil will be used to refer to a mixture of heavy compounds including water, higher alcohols, methanol, and alkanes. Conversely, the term light ends hydrocarbons will be used to refer to gaseous products that are lighter than methanol.

[0042] According to another embodiment of the invention, the preheating step is carried out in a conventional heat exchanger or an electric heater and the temperature conditioned stream is mixed with the first stream of fusel oil recovered from the refining process before being conveyed to the reforming process.

[0043] According to a particularly interesting application of the invention, said second stream of synthesis gas resulting from the reforming process before being mixed with said first stream of synthesis gas is subjected successively to a cooling step by a recovered aqueous stream produced in the purification step and to a separation step for condensing the condensed water.

[0044] Preferably, the condensed water is mixed with the aqueous stream recovered from the purification step before being heat exchanged with the second stream of synthesis gas in the cooling step.

[0045] According to one embodiment, the cooling step includes a steam generation step, in which the second stream of light ends hydrocarbons from the refining section and the mixture of flash gas and tail gas from the methanol synthesis loop are combusted to generate superheated steam. Preferably, the combustion conditions in the steam generation step are established by a fired heater.

[0046] Alternatively, superheated steam can be generated in the steam generation step by combusting the first stream of fusel oil, the second stream of light ends hydrocarbons, and a mixture of the flash gas and tail gas.

[0047] Certain embodiments of the invention relate to the use of various purge streams of the methanol synthesis process. Typically, purge gas is extracted from the methanol synthesis loop to avoid accumulation of inert gases, and the purge gas, possibly after washing with water, is passed to a hydrogen recovery unit (HRU) to recover the hydrogen contained therein, producing a stream of recovered hydrogen and a tail gas, referred to as HRU tail gas. The HRU tail gas may contain residual hydrogen and methane. Additional purge streams from the methanol process include flash gas from one or more separators, light ends and fusel oil from crude methanol distillation. In certain embodiments, at least a portion of the HRU tail gas is recycled as process gas to the reforming section. Other purge streams and optionally a remaining portion of the HRU tail gas can be recycled as fuel to the fired heaters.

[0048] In an interesting embodiment of the invention, the HRU tail gas provides a major part of the process feed of the reforming step, or more preferably the entire process feed of the reforming step. In the latter case, a major advantage of the invention is that no additional fossil fuel is required for the reforming step. It can be said that the reforming step is carried out consecutively to the gasification step.

[0049] For example, according to an embodiment of the present invention, the autothermal reformer's process supply is provided entirely by tail gas removed from the methanol synthesis process supplied by the gasifier, so that the autothermal reformer and gasifier can be considered to operate continuously.

[0050] Preferably, the HRU tail gas provides at least 80%, or at least 90%, or even more preferably 100% of the process feed for the reforming step.

[0051] Particularly preferably, the reforming step is carried out in an autothermal reformer where the process feed is provided entirely by methanol tail gas. In another embodiment, the reforming step is carried out in a partial oxidation reactor.

[0052] The HRU tail gas may be fed to the reforming process after appropriate treatment, which preferably includes saturation with water and may also include preheating.

[0053] According to another interesting feature of the invention, the reforming step includes preheating the process stream to be reformed in a fired heater whose fuel is provided, at least in part, by one or more of the purge streams mentioned above, and possibly also by a small amount of HRU tail gas.

[0054] Particularly preferably, the fired heater is fuelled with the purge stream and also with a portion of the make-up gas of the methanol synthesis loop acting as a trim fuel to ensure controlled combustion.More preferably, for safety reasons, a natural gas stream is supplied to the pilot burner of the fired heater.

[0055] In a preferred embodiment, the reforming step is carried out in an autothermal reformer, the process feed at the inlet of which comprises at least 20 mol% methane on a dry basis, preferably equal to or about 50 mol% methane on a dry basis.

[0056] In embodiments based on autothermal reforming, the reforming section preferably includes an autothermal reformer as the only catalytic reactor in the reforming section.

[0057] According to the invention, the plant comprises a gasification section configured to convert biomass feedstock into a gasifier stream in the presence of water steam and an oxidant, a front end including a water-gas shift converter for obtaining a first stream of synthesis gas carrying hydrogen, carbon monoxide and residual CO2, and a CO2 removal section.

[0058] The plant further comprises a methanol synthesis loop, a tail gas treatment section, and a line with a compression unit connecting the methanol front end and the methanol synthesis loop.

[0059] The methanol synthesis loop includes a methanol synthesis reactor configured to produce crude methanol and a tail gas.

[0060] A tail gas processing section connects a methanol synthesis loop and the line connecting the methanol front end and the methanol synthesis loop.

[0061] The tail gas processing section includes a water saturation tower in communication with the methanol synthesis loop and configured to produce a saturated water stream, a preheat unit in communication with the saturation tower, and a reforming unit in fluid communication with the preheat unit and configured to produce a second stream of synthesis gas.

[0062] The plant further comprises a line connecting said reforming unit and said compressor unit.

[0063] The plant may further include a line configured to supply steam to the saturated water stream prior to the preheat unit, and a purification section in communication with the methanol synthesis loop.

[0064] Preferably, the refining section is a multi-column distillation section and is configured to produce a methanol product, a recovered aqueous stream, a first stream of fusel oil, and a second stream of light ends hydrocarbons.

[0065] According to one embodiment, the plant further comprises a line connecting said preheating unit and said purification section, said preheating unit being a fired heater and said reforming unit being an autothermal reformer.

[0066] Alternatively, the plant further comprises a line connecting said purification section and said reforming section, said reforming section being a partial oxidation reactor.

[0067] Preferably, when the reforming unit is a partial oxidation reactor, the preheat unit is a conventional heat exchanger or an electric heater, and conversely, when the reforming unit is an autothermal reformer, the preheat unit is an electric heater or a fired heater.

[0068] According to a different embodiment, when the preheat unit is a fired heater, the latter can be fired with a mixture of said first stream of fusel oil, said second stream of light ends hydrocarbons and said flash gas and tail gas.

[0069] The plant preferably includes a cooling section disposed downstream of the reforming unit and including a steam generation section with a fired heater in fluid communication with the methanol synthesis loop and the purification section.

[0070] The methanol synthesis loop preferably comprises a methanol reactor with a fixed bed operating in the pressure range of 50-120 bar and in the temperature range of 200-300°C.

[0071] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a methanol plant 100 for the synthesis of methanol 1, including a front end 101, a methanol synthesis loop 19, a purification section 21 and a tail gas processing section 102.

[0072] The methanol front end 101 consists of a pretreatment section 3, a gasifier 6, a gas scrubbing unit 8, a water gas shift reactor 10, and a carbon dioxide CO2 removal unit 14.

[0073] The tail gas processing section 102 includes a water saturation tower 36 in communication with the methanol synthesis loop 19, a preheat unit, and a reforming unit. In the embodiment of Figure 1, the preheat unit includes a fired heater 23, and the reforming unit includes an autothermal reformer 25. The gas processing section 102 further includes a cooling section 50 and a condenser 30.

[0074] Air separation unit 47 provides oxygen-containing streams 48 , 49 to gasifier 6 and autothermal reformer 25 .

[0075] The methanol synthesis loop 19 and the purification section 21 each comprise a methanol synthesis reactor and a distillation unit (not shown). The methanol synthesis loop 19 and the purification section 21 are in communication with each other by a line 51 carrying a crude methanol stream 20.

[0076] The methanol synthesis process will now be described with reference to Figure 1. Biomass feedstock 2 is fed to a pre-treatment section 3 where the humidity of the feedstock 2 is reduced to an appropriate level to obtain dried biomass 4.

[0077] The dried biomass 4 is fed to a gasifier 6 in the presence of water steam 5 and oxygen 48 to produce a gasifier stream 7. The gasifier stream 7 is then conveyed to a gas scrubbing unit 8 where impurities such as sulfur and alkali are removed to produce a purified gas 9. The purified gas 9 is then fed to a water gas shift reactor 10 where the S / C ratio of the purified gas 9 is adjusted to a value suitable for methanol synthesis to produce a conditioned make-up gas 13.

[0078] The conditioned make-up gas 13 is then treated in a CO2 removal unit 14. The output of the CO2 removal unit 14 is a first stream of synthesis gas 15, which is mixed with a second stream of synthesis gas 31 extracted from a condenser 30 to obtain a third stream of synthesis gas 16. Said third stream 16 is suitable for conversion in a methanol synthesis loop and constitutes the methanol make-up gas.

[0079] Methanol make-up gas 16 is sent to the suction section of compressor 17 to obtain compressed make-up gas 18 which is fed to methanol synthesis loop 19.

[0080] In the methanol synthesis loop 19, crude methanol 20 is synthesized under methanol synthesis conditions. Other effluents of the methanol synthesis loop 19 are tail gas 35 and a mixture of flash gas and tail gas 34. Both the tail gas 35 and the mixture of flash gas and tail gas 34 are gaseous streams that carry methane. The tail gas in lines 34 and 35 may be taken from a hydrogen recovery unit that processes purge gas removed from the methanol synthesis loop.

[0081] The crude methanol 20 is then conveyed to a refining / distillation section 21 to produce a pure methanol product 1, a recovered aqueous stream 33, a first stream of fusel oil 40, and a second stream of light ends hydrocarbons 41.

[0082] Tail gas 35 is fed to saturator 36 where it is saturated with hot water 43 to produce saturated stream 37 .

[0083] Saturated steam 37 is then contacted with steam 38 to produce conditioned stream 39 which is preheated in fired heater 23 and fed to autothermal reformer 25 after preheating. This stream 39 represents the total feed to autothermal reformer 25.

[0084] The fired heater 23 is fired with the flash gas and tail gas mixture 34, the first stream of fusel oil 40, and the second stream of light ends hydrocarbons. The output of the fired heater 23 is conditioned stream 24, which is then conveyed to an autothermal reformer 25.

[0085] The output of the autothermal reformer 25 is a reformed gas 26 which is fed in turn to a cooling section 50 and a condenser 30 to obtain a condensed water 32 and a second stream 31 of said synthesis gas.

[0086] The second stream of syngas 31 is then mixed with the first stream of syngas 15 from the CO2 removal unit 14, as described above.

[0087] The cooling section 50 comprises a steam generation section 27 and one or more heat exchangers 28. The recovered aqueous stream 33 from the purification section 21 is fed to the heat exchanger 28 in heat exchange with a cooled gas effluent 53 of the steam generation section 27. The heat exchanger 28 produces a hot water stream 43 which is conveyed to the saturation tower 36, and a cooled gas stream 29 exiting the heat exchanger 28 is fed to the condensation section 30.

[0088] As is evident from the above embodiment, all resources generated in the process are recycled within the process, namely the tail gas 35 and the recovered aqueous stream 33. To avoid the accumulation of impurities present in the distilled water, a purge stream can be discharged to the bottom of the saturation tower.

[0089] Advantageously, by virtue of the above-described configuration, applicants have discovered that methanol productivity can be increased by approximately 30% compared to conventional biomethanol processes in which the tail gas 35 and recovered aqueous stream 33 are not recycled within the process.

[0090] Additionally, the carbon efficiency, calculated as moles of pure CH3OH in crude CH3OH / moles (CO+CO2+CH4) in make-up gas, increased from 72% to 93%.

[0091] 2 shows a methanol plant 100 according to an alternative embodiment of the invention. This embodiment differs from FIG. 1 in that it uses a partial oxidation reactor (POX reactor) 125.

[0092] A first stream of synthesis gas 15 is synthesized according to the process previously described, where said first stream of synthesis gas 15 is mixed with said second stream of synthesis gas 31 and compressed in compressor 17 to obtain compressed gas 18 which is fed to a methanol synthesis loop 19.

[0093] The outputs of the methanol synthesis loop are a flash gas and tail gas mixture 34, a crude methanol stream 20, and tail gas 35. The crude methanol stream 20 is fed to a refining section 21 which produces a methanol product 1, a recovered aqueous stream 33, a first fusel oil stream 40, and a second light ends hydrocarbon stream 41.

[0094] As with the previous embodiment, the tail gas is fed to saturator 36 to produce saturated gas 37 which is then mixed with steam 38 to produce conditioned stream 39 .

[0095] Conditioned stream 39 is then conveyed to preheat unit 23 , which in this embodiment is represented by a conventional heat exchanger or an electric heater, to ultimately produce temperature conditioned stream 24 .

[0096] The temperature conditioned stream 24 is then mixed with the first fusel oil stream 40 to obtain a gas product 55 which is then conveyed to the partial oxidation reactor 125 .

[0097] The product of the partial oxidation is reformed gas 26 which is then processed in a cooling step 50. The cooling step comprises a steam generation section 27 and a heat exchanger 28. The steam generation section includes a fired heater (not shown) fired with fuel gas 44 obtained by mixing the second stream 41 of light ends hydrocarbons with the mixture 34 of flash gas and tail gas.

[0098] As with the previously described embodiment, the recovered aqueous stream 33 exiting the purification section 21 is fed to a heat exchanger 28 where it indirectly exchanges heat with the gaseous exhaust 53 of the steam generation section 27 .

[0099] The output of heat exchanger 28 is hot water stream 43 and cooled stream 29. Hot water stream 43 is conveyed to saturator 36 and cooled stream 29 is sent to syngas wash condensing section 30.

[0100] The output of the condensation section 30 is a condensed water 32 and the second stream of syngas 31. The condensed water 32 is mixed with the recovered aqueous stream 33 and then passed through heat exchanger 28 to produce hot water 43 which is fed to saturator 36.

[0101] FIG. 3 illustrates an embodiment in which the steam generation section 27 includes a fired heater fired with a mixture of flash gas and tail gas 34, a first stream of fusel oil 40, and a second stream of light ends hydrocarbons 41.

[0102] In a further embodiment of the present invention, the preheat unit 23 to which the conditioned flow 39 is supplied may be an electric heater.

Claims

1. A process (100) for the synthesis of methanol (1), a) A step of subjecting a biomass raw material (2) to a gasification process (6) in the presence of steam (5) and an oxidizing agent (48) to generate a gasification device flow (7); b) A step of subjecting the gasification apparatus flow (7) to a water-gas shift conversion (10), and then to a CO2 removal step (14) to obtain a first flow (15) of synthesis gas that retains hydrogen, carbon monoxide, and CO2; c) A step of mixing the first stream (15) of synthesis gas with the second stream (31) of synthesis gas to obtain a third stream (16) of synthesis gas; d) A step of supplying the third stream (16) of the synthesis gas to a methanol synthesis loop (19) in which the catalytic conversion of carbon oxides to methanol is carried out under methanol synthesis conditions, thereby obtaining crude methanol (20) and a tail gas (35) that retains methane; e) The tail gas (35) is subjected to a reforming step (25) in the presence of an oxidizing agent (49) to generate the second flow (31) of the synthesis gas in step c), and Includes, Step e) includes subjecting the tail gas (35) obtained in step d) to a saturation step (36) with water (43) to obtain a saturated flow (37), and then subjecting the saturated flow (37) to water vapor (38) to obtain a modified flow (39), and then subjecting the modified flow (39) to the reforming step (25), The crude methanol (20) is further subjected to a purification step (21) to produce a methanol product (1), a first stream of fusel oil (40), a second stream of light-end hydrocarbons (41), and a recovered aqueous stream (33), and the recovered aqueous stream (33) is subjected to the saturation step (36). Process (100) for the synthesis of methanol (1).

2. The process according to claim 1, wherein the modification step (25) of point e) is carried out under self-thermal modification conditions or partial oxidation conditions.

3. The process according to claim 1, wherein at least one of the oxidizing agent (48) in step a) and the oxidizing agent (49) in step e) is an oxygen stream having a purity of more than 99 mol%.

4. The process according to claim 3, wherein at least one of the oxidizing agent (48) in step a) and the oxidizing agent (49) in step e) is an oxygen stream having a purity of more than 99.5 mol%.

5. The process according to claim 4, wherein the adjusted flow (39) has a water vapor-to-carbon ratio S / C that is between 1.0 and 2.

0.

6. The process according to claim 1, wherein the adjusted flow (39) before being supplied to the modification step (25) is preheated in a preheating stage (23) to obtain a temperature-controlled flow (24) having a temperature in the range of 600 to 750°C.

7. The process according to claim 6, wherein the adjusted flow (39) before being supplied to the modification step (25) is preheated in a preheating stage (23) to obtain a temperature-controlled flow (24) having a temperature of 650°C.

8. The process according to claim 6, wherein a further product of the methanol synthesis loop (19) is a gas mixture (34) of flash gas and tail gas, the preheating stage (23) is carried out under direct combustion conditions and is combusted by a first flow (40) of fusel oil, by a second flow (41) of light-end hydrocarbons, and by the gas mixture (34) of flash gas and tail gas.

9. The process according to claim 6, wherein the temperature-controlled flow (24) is mixed with a first flow (40) of fusel oil recovered from the refining step (21) before being transported to the modification step (25).

10. The process according to claim 1, wherein the second stream (31) of the synthesis gas in step c) prior to being mixed with the first stream (15) of the synthesis gas is subsequently subjected to a cooling step (50) and a separation step (30) to condense into condensate (32) together with the recovered aqueous stream (33) produced in the purification step (21).

11. The process according to claim 10, wherein the condensed water (32) is mixed with the recovered aqueous stream (33) from the purification step (21) before it exchanges heat with the second stream (31) of the synthesis gas in the cooling step (50).

12. The process according to claim 10, wherein the cooling step (50) includes a steam generation step (27), and the mixed gas (34) of flash gas and tail gas, the second flow (41) of the right-end hydrocarbon, and optionally the first flow (40) of the fusel oil are burned in the steam generation step (27) to produce superheated steam.

13. The process according to claim 1, wherein the tail gas (35) provides at least 80% or all of the process supply for the reforming step (e).

14. The process according to claim 1, wherein the reforming step includes preheating of a process flow to be reformed in a combustion heater, the fuel for the combustion heater includes one or more purge flows taken out from the synthesis of crude methanol and / or purge flows taken out from the purification of crude methanol, and the fuel for the combustion heater optionally includes one or more of the following: a portion of tail gas (35); a portion of the third flow (16) of the synthesis gas in step d); and a flow of natural gas.

15. The process according to any one of claims 1 to 14, wherein the reforming step (e) is carried out in a self-thermal reformer (25), and the process feed of the self-thermal reformer contains at least 20 mol% methane on a dry basis.

16. The process according to claim 15, wherein the reforming step (e) is carried out in a self-thermal reformer (25), and the process feed of the self-thermal reformer contains 50 mol% methane on a dry basis.

17. A plant for producing methane, a) A front end (101) comprising a gasification section (6) configured to convert a biomass raw material (2) into a gasification flow (7) in the presence of steam (5) and an oxidizer (48), a water-gas shift converter (10), and a CO2 removal section (14), which obtains a first flow (15) of synthesis gas that retains hydrogen, carbon monoxide, and CO2; b) A methanol synthesis loop (19) comprising a methanol synthesis reactor configured to produce crude methanol (20) and tail gas (35); c) A line comprising a compression unit (17) connecting the methanol front end (101) to the methanol synthesis loop (19); d) The methanol synthesis loop (19) is connected to the line connecting the methanol front end (101) and the methanol synthesis loop (19) by a tail gas treatment section (102), - A water saturation tower (36) located downstream of the methanol synthesis loop (19) and configured to produce a saturated flow (37); - A preheating unit (23) that communicates with the saturation tower (36); - A reforming unit (25) that is in communication with the preheating unit (23) and configured to produce a second flow (31) of synthesis gas; - A line connecting the modification unit (25) to the compression unit (17), Tail gas treatment section including It is equipped with, and furthermore, A line configured to supply steam (38) to the saturated flow (37) in front of the preheating unit (23); A purification section (21) communicating with the methanol synthesis loop (19), wherein the purification section (21) is a multi-column distillation section and is configured to produce a methanol product (1), a recovered aqueous stream (33), and a first stream (40) of fusel oil and a second stream (41) of light-end hydrocarbons; and A line supplying the recovered aqueous flow (33) to the water saturation tower (36) A plant equipped with methane-producing features.

18. The preheating unit (23) includes a line connecting it to the refining section (21), and the preheating unit (23) is a combustion heater, and the reforming unit (25) is a self-heat reformer, or The purification section (21) includes a line connecting it to the reforming unit (25), and the reforming unit is a partial oxidation reactor. The plant according to claim 17.

19. The plant according to claim 17 or 18, further comprising a cooling section (50) including a steam generating section (27) located downstream of the reforming unit (25) and having a combustion heater in fluid communication with the methanol synthesis loop (19) and the purification section (21).

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